The main shaft in a gas turbine engine is supported by one or more sets of bearings. While these bearings must be lubricated to ensure continuous and efficient operation of the engine, it is also desirable to minimize the extent to which the bearing chamber may leak lubricant. Not only can leaked lubricant potentially contaminate nearby systems, but undetected leakage can also eventually lead to engine failure or damage. In addition to oil leakage, any leakage of high-temperature air into the bearing chamber could severely damage the bearings and compromise engine operation.
Bearing chamber pressurization is often used in gas turbine engines (including ground based generator and derivatives thereof) to improve the effectiveness of the bearing chamber seals to maintain lubricant within the chamber, and in general, bearing chamber pressurization enhances the ability of the seals to prevent oil from leaking from the bearing chamber and to prevent high-temperature air from penetrating into the bearing chamber. In particular, oil sump seals prevent leakage of lubricating oil into the main flow path of air and combustion gases through the engine. Buffer seal arrangements allow a portion of the compressed air produced by a compressor stage to be diverted into a buffer chamber or plenum within the engine. This buffered flow is then directed from the buffer chamber to locations close to sump seals to provide a pressure barrier against oil leakage. However, leakage may eventually occur nonetheless due to wear and degradation of the seals and/or due to problems in the buffer system.
While it is sometimes possible to redirect any oil leakage away from critical systems such as compressors for cabin air pressure and the like, this strategy does not avoid damage to the bearing or shaft itself should the leakage continue undetected or increase in severity. Indeed, typical lubricant leaks do not decrease in severity, and are typically detected only indirectly when they are substantial enough to cause noticeable excess oil consumption, or to cause main oil pressures exceeding high or low limits. Moreover, typical lubrication and buffer system sensitivities mean that excessive seal wear or failure in certain bearing compartment locations will not cause a significant enough change in the typically monitored engine parameters (main oil pressure, oil temperature, oil filter delta-P, oil quantity) to be detected without engine removal and partial disassembly.
As such, there is a continued need for an improved bearing seal leak detection system that can detect very slight amounts of wear and allow maintenance and repair before more significant damage occurs, without requiring frequent disassembly of the engine to visually inspect the seals. It will be appreciated that this background section was created by the inventors for the reader's convenience, and is meant to discuss problems and solutions noted by the inventors, not to discuss or explain prior art. Thus the inclusion of any problem or a solution in this section is not an indication that the problem or a solution is prior art.